We consider a single-anchor multiple-input multiple-output orthogonal frequency-division multiplexing system with imperfectly synchronized transmitter (Tx) and receiver (Rx) clocks, where the Rx estimates its position based on the received reference signals. The Tx, having (imperfect) prior knowledge about the Rx location and the surrounding geometry, transmits reference signals based on a set of fixed beams. We develop strategies for the power allocation among the beams aiming to minimize the expected Cramér-Rao lower bound for Rx positioning. Additional constraints on the design are included to make the optimized power allocation robust to uncertainty on the line-of-sight (LOS) path direction. Furthermore, the effect of clock asynchronism on the proposed allocation strategies is studied. Our evaluation results show that, for non-negligible synchronization error, it is optimal to allocate a large fraction of the available power for the illumination of the non-LOS (NLOS) paths, which help resolve the clock offset. In addition, the complexity reduction achieved by our proposed suboptimal approach incurs only a small performance degradation. We also propose an off-grid compressed sensing-based position estimation algorithm, which exploits the information on the clock offset provided by NLOS paths, and show that it is asymptotically efficient.

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In this work, we study optimal transmit strategies for minimizing the positioning error bound in a line-of-sight scenario, under different levels of prior knowledge of the channel parameters. For the case of perfect prior knowledge, we prove that two beams are optimal, and determine their beam directions and optimal power allocation. For the imperfect prior knowledge case, we compute the optimal power allocation among the beams of a codebook for two different robustness-related objectives, namely average or maximum squared position error bound minimization. Our numerical results show that our lowcomplexity approach can outperform existing methods that entail higher signaling and computational overhead.

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Availability of abundant spectrum has enabled millimeter wave (mm-wave) as a prominent candidate solution for the next generation cellular networks. Highly directional transmissions are essential for exploitation of mm-wave bands to compensate high propagation loss and attenuation. The directional transmission, nevertheless, necessitates a specific design for mm-wave initial cell discovery, as conventional omni-directional broadcast signaling may fail in delivering the cell discovery information. To address this issue, this paper provides an analytical framework for mm-wave beamformed cell discovery based on an information theoretical approach. Design options are compared considering four fundamental and representative broadcast signaling schemes to evaluate discovery latency and signaling overhead. The schemes are then simulated under realistic system parameters. Analytical and simulation results reveals four key findings: (i) For cell discovery without knowledge of beacon timing, analog/hybrid beamforming performs as well as digital beamforming in terms of cell discovery latency; (ii) Single beam exhaustive scan optimize the latency, however leads to overhead penalty; (iii) Multi-beam simultaneous scan can significantly reduce the overhead, and provide the flexibility to achieve trade-off between the latency and the overhead; (iv) The latency and the overhead are relatively insensitive to extreme low block error rates. ) 2 I. INTRODUCTIONMillimeter wave (mm-wave) frequency bands between 6 and 100 GHz have drawn significant attention for the next generation cellular communication systems [1][2], where the available bandwidths are much wider than today's cellular allocations [3][4]. Mm-wave signals, however, suffer from increased isotropic free space loss, higher penetration loss, and propagation attenuation, resulting in outages and intermittent channel quality [5]. In this regard, enhanced antenna gain is required at both transceiver sides to completely compensate the loss and the attenuation of mm-wave transmissions.Fortunately, the very small wavelengths of the mm-wave signals, combined with advanced low power CMOS RF circuits, enable the deployment of large-scale miniaturized antennas and the exploitation of beamforming and spatial multiplexing [6]. As a result, reliance of highly directional transmission and reception considerably complicates initial cell discovery in mm-wave cellular communications. While conventional cellular systems, such as 3GPP LTE/LTE-A [7]-[9], support multi-antenna diversity techniques and spatial multiplexing with beamforming, underlying design assumption is that the initial cell discovery can be conducted entirely with omni-directional transmissions or transmissions in fixed antenna patterns [10]. LTE base station (BS), for example, generally does not apply beamforming when transmitting synchronization and broadcasting signals. Directional transmissions are typically exploited only after initial access has been established.Moreover, for mm-wave communications, omni-directional bro...

We study the performance bounds of vehicle-tovehicle (V2V) relative positioning for vehicles with multiple antenna arrays. The Cramér-Rao bound for the estimation of the relative position and the orientation of the Tx vehicle is derived, when angle of arrival (AOA) measurements with or without timedifference of arrival (TDOA) measurements are used. In addition, geometrically intuitive expressions for the corresponding Fisher information are provided. The derived bounds are numerically evaluated for different carrier frequencies, bandwidths and array configurations under different V2V scenarios, i.e. overtaking and platooning. The significance of the AOA and TDOA measurements for position estimation is investigated. The achievable positioning accuracy is then compared with the present requirements of the 3rd Generation Partnership Project (3GPP) 5G New Radio (NR) vehicle-to-everything (V2X) standardization.

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